It is likely that you can export GWB files as PDF documents using the InterWrite Reader software. You may as well use the File ► Print function to print it as PDF file instead on paper.
Convert InterWrite Reader file to Adobe Portable document format.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert gwb to pdf on Windows
A software for eading and printing of GWB format
Convert from gwb file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.